A novel frontier in the treatment of tumors is oncolytic virotherapy, whereby a replication competent virus infects the tumor cells, spreads from cell to cell of the tumor and destroys them. Two such tumors are mammary and ovary cancers, that afflict animals such as humans. About 30% of human mammary tumors, as well as some ovary tumors, are highly malignant and metastatic.
These tumors owe their high malignancy and metastaticity to the expression of a specific cell surface molecule receptor, named HER2, that belongs to the family of epidermal growth factor receptors, and are generally treated with surgery or combined surgery and radiotherapy or chemiotherapy.
HSV is a pathogen virus for mammalian cells [HSV-1 is e.g. described in Ejercito, P. M., et al. (1968). J Gen Virol 2:357 and its genome has accession number NC-001806 (GenBank)].
HSV enters cells by a multistep process. The first step is attachment to the cell surface, mediated by interaction the glycoproteins gB and gC (Laquerre S., Argnani R., Anderson D. B., Zucchini S., Manservigi R., Glorioso J. C. (1998), J. Virol. 72(7):6119-30). This is followed by the more specific interaction of the virion envelope glycoprotein D (gD) with one of its entry receptors: nectin1/HveC, HVEM/HveA, and O-linked sulphated moieties of heparan sulphate (Spear P. G., Eisenberg R. J., Cohen G. H., (2000) Virology 275:1-9) (Campadelli-Fiume G., Cocchi F., Menotti L., Lopez M. (2000) Reviews in Medical Virology, 10:305-319) (Campadelli-Fiume G. et al. (2007) Rev. Med. Virol., 17:313-326) (the GenBank codes for the receptors are the followings: nectin1 alpha AF060231, nectin1 beta AF110314, HVEM U70321).
In recent years, there have been attempts to use genetically engineered HSVs as oncolytic agents mainly to treat malignant glioma. Inasmuch as wild-type viruses are virulent, target and destroy many different cells and tissues, the candidate oncolytic HSVs have been highly attenuated. The viruses that have reached clinical trials were made dependent for their replication upon the dividing tumor cell by the deletion of two HSV genes, namely the gamma1 43.5 gene—which encodes the ICP34.5 protein whose role is to preclude the shut off of protein synthesis in infected cells, and the UL39 gene—which encodes the large subunit of ribonucleotide reductase. These viruses are marred by low ability to replicate, even in dividing cells, a feature that results in two negative effects. First, administration of such viruses to tumors fails to produce high yield of progeny viruses, capable of spreading from cell to cell of the tumor itself, and thus to amplify the response to any given therapeutic dose of the virus. Second, the viruses are difficult to grow and can hardly be produced in large scale (108-109 plaques forming units PFU/ml) to yield the amount of virus required for clinical applications. Furthermore, the preserved ability of the virus to bind to any cell bearing one the natural receptors for the HSV subtracts the virus to the tumor tissues that most need it and diminishes the therapeutic effect of tumor cell killing, and may exert undesired infection of non cancer tissues and cells, including their death by apoptosis. We note that, even if these viruses were retargeted to tumor-specific receptors—they are nonetheless highly attenuated.
Recently HSV retargeted to specific receptors have been genetically engineered so that they can infect cells that need to be destroyed while maintaining high capacity to replicate and spread from cell to cell. Though such viruses have a good ability to spread among tumor cells, they still undesirably infect non cancer tissues and cells.
Patent application having publication number WO2004/033639, whose content is herein fully included, discloses a recombinant HSV, which expresses on its glycoproteic envelope a natural cytokine. Though the use of recombinant HSV of this type has been proposed for treating tumors, it is important to stress that: the targeted receptor has natural ligand of a small size such that it can be readily inserted in gD, and the proposed recombinant HSV is still capable of interacting with receptors nectin1/HveC and HVEM/HveA. In particular, WO2004/033639 fails to identify mutations that would result in a recombinant HSV which is not anymore capable of binding nectin1/HveC and is capable of binding receptors (such as HER2/ErbB2) of diseased cells.
It follows that a need in the art still exists for viral therapeutic agents targeting selectively cells that need to be destroyed. In particular a need exists for viral therapeutic agents targeting receptors that have no natural ligand, and are overexpressed or selectively expressed in diseased cells, such as cancer cells.